Field of the Invention
This invention generally relates to compositions comprising cationically polymerizable materials which are curable in a short time, e.g., fixturing in approximately one minute or less and reaching full properties within a short time thereafter, in the manner of cyanoacrylates.
More specifically, the present invention relates to curable compositions comprising cationically polymerizable materials wherein rapid cure is achieved by the in situ generation of cations, which function as catalytic species for the cure of such materials, and to two-component adhesive compositions which in use are applied one component to each of two matable surfaces with rapid cure occurring on mating of the surfaces.
Description Of The Related Art
As discussed in our copending U.S. patent application Ser. No. 669,189, filed Nov. 7, 1984 and now issued as U.S. Pat. No. 4,565,837, a major disadvantage of prior art fast cure epoxies curable at room temperature conditions, e.g., mercaptan cured epoxies, is that rapid gellation of such materials retards the development of full properties due to the restriction of molecular motion and the cure mechanism involved. Extremely fast cures in these compositions result in overly plasticized products due to the need to use a high level of the curative component. Further, for conventional amine- or mercaptan-cured epoxies, there is a critical mix ratio or stoichiometry for the epoxy resin/curing agent (hardener) mixture, with thorough mixing necessary to achieve full cure.
In the aforementioned copending patent application, we have described storage stable dispersions of stable carbocation salts as initiators for polymerizing epoxy resins to high molecular weight solids. Specifically disclosed in such application are two-part adhesive compositions of a type exhibiting rapid room temperature cure, which in a first part comprise an oxirane functional resin and in a second part comprise a stable carbenium ion salt, i.e., a triphenylmethyl or tropylium salt in a suitable carrier.
In epoxy compositions of the type exemplified in the above-described application, carbocation initiators cause spontaneous epoxy polymerization and thus generally are dispersed in an unreactive carrier; as such, the respective components require thorough mixing to produce a homogeneous polymeric solid. In many instances, the requirement of such thorough mixing is at odds with the rapid cure nature of the composition, and may result in premature fixturing of the composition prior to its application to the desired substrate.
Illustrative of the prior art usage of other curing agents which effect spontaneous polymerization when mixed with a separate epoxy resin component are U.S. Pat. No. 4,396,754, which teaches an epoxy curing catalyst selected from lithium or Group II metal salts of a non-nucleophilic acid, including LiBF.sub.4, Ca(BF.sub.4).sub.2, Mg(BF.sub.4).sub.2, LiPF.sub.6, Ca(PF.sub.6).sub.2, Mg(PF.sub.6).sub.2, LiSbF, LiAsF.sub.6 and the like, and U.S. Pat. No. 4,092,296, which teaches to utilize metallic fluoroborate salts, e.g., salts of tin, copper, zinc, nickel, lead and silver, in aqueous solution as epoxy curing agents. See also U.S. Pat. Nos. 4,069,055 and 4,138,255 to J. V. Crivello which disclose the cationic polymerization of epoxy resins by radiation sensitive aromatic onium salts of Group VA and VIA.
The aforementioned U.S. Pat. No. 4,092,296 teaches the use of silver tetrafluoroborate but shows it by example to be a poor single catalyst (Examples 192-197; see column 23, line 51-column 24, line 22). All other metallic salts disclosed in U.S. Pat. Nos. 4,396,754 and 4,092,296 are characterized by short shelf lives due to their activity as single catalysts, i.e., their spontaneous high reactivity with epoxy resins.
Accordingly, it would be a substantial advance in the art to provide an epoxy adhesive composition wherein the catalyst, i.e. hardening agent, is generated in situ in a manner facilitating the application of the composition to the substrate materials without premature curing.
It therefore is an object of the present invention to provide a composition comprising a cationically polymerizable material, e.g., an oxirane functional resin, which is rapidly cured and reaches full properties in a short time, but does not require the complete mixing of components in the manner of prior art two-part epoxy resin systems.
It is another object of the present invention to provide a cationically polymerizable resin composition comprising two parts, wherein each part contains an integral component of the catalyst system for the resin.
Other objects and advantages of the present invention will be apparent from the ensuing disclosure and appended claims.